The semiconductor integrated circuit (IC) industry has experienced rapid growth. Modern integrated circuits are made up of literally millions of active devices such as transistors and capacitors. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. These devices are initially isolated from each other, but are later interconnected together through multiple metal layers to form functional circuits. As the IC becomes increasingly more complex, the interconnect structure also becomes more complex, resulting in increasing number of metal layers.
Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as conductive vias and contacts. Complex interconnects can limit performance and the density of modern integrated circuits. Tantalum (Ta) has been used as a barrier layer material around copper conductors to block the diffusion of conductive copper into a surrounding inter-layer dielectric (ILD) layer. Copper readily diffuses during operation in a phenomenon known as electromigration. Electromigration can produce tendrils that can short adjacent conductive features. However, Ta as deposited using current techniques exhibits a contact resistivity (Rc) that is much higher than that of copper. Thus, the Ta barrier layer limits the overall line resistance. Hence, what is needed are structures and methods of forming an interconnect structure with the blocking advantage of Ta barrier layer without disadvantage of lower Rc performance.